One of the drawbacks inhibiting the introduction of a gasoline Homogeneous Charge Compression Ignited (HCCI) engine in production has been the lack of a simple, cost effective, and energy-efficient Variable Valvetrain Actuation (VVA) system to vary one or both of the exhaust and intake events. Many electro-hydraulic and electro-mechanical VVA systems have been proposed for gasoline HCCI engines, but while these systems may consume less or equivalent actuation power at low engine speeds, they typically require significantly more power than a conventional fixed-lift and fixed-duration valvetrain system to actuate at mid and upper engine speeds. Moreover, the cost of these systems can approach the cost of an entire conventional engine itself.
As the cost of petroleum continues to rise from increased global demands and limited supplies, the fuel economy benefits of internal combustion engines will become a central issue in their design, manufacture, and use at the consumer level. In high volume production applications, applying a continuously variable valvetrain system to just the intake side of a gasoline engine in an Early Intake Valve Closing (EIVC) strategy can yield fuel economy benefits up to 10% on Federal Test Procedure—USA (FTP) or New European Driving Cycle (NEDC) driving schedules, based on simulations and vehicle testing. HCCI type combustion processes have promised to make the gasoline engine nearly as fuel efficient as a conventional, 4-stroke Diesel engine, yielding gains as high as 15% over conventional (non-VVA) gasoline engines for these same driving schedules. The HCCI engine could become strategically important to the United States and other countries dependent on a gasoline-based transportation economy.
Likewise, the use of a continuously variable valvetrain for both the intake and exhaust sides of a Diesel engine has been identified as a potential means to reduce the size and cost of future exhaust aftertreatment systems and a way to restore a portion of the lost fuel economy that these systems presently impose. By varying the duration of intake lift events, potential Miller cycle-type fuel economy gains are feasible. Also, with VVA on the intake side, the effective compression ratio can be varied to provide a high ratio during startup and a lower ratio for peak fuel efficiency at highway cruise conditions. Without intake side VVA, compression ratios must be compromised in a tradeoff between these two extremes. Exhaust side VVA can improve the torque response of a Diesel engine. Varying exhaust valve opening times can permit faster transitions with the turbocharger, thereby reducing turbo lag. Exhaust VVA can also be used to expand the range of engine operation wherein pulse turbo-charging can be effective. Furthermore, varying exhaust valve opening times can be used to raise exhaust temperatures under light load conditions, significantly improving NOx adsorber efficiencies.
VVA devices for controlling the timing of poppet valves in the cylinder head of an internal combustion engine are well known.
For a first example, U.S. Pat. No. 5,937,809 discloses a Single Shaft Crank Rocker (SSCR) mechanism wherein an engine valve is driven by an oscillatable rocker cam that is actuated by a linkage driven by a rotary eccentric, preferably a rotary cam. The linkage is pivoted on a control member that is in turn pivotable about the axis of the rotary cam and angularly adjustable to vary the orientation of the rocker cam and thereby vary the valve lift and timing. The oscillatable cam is pivoted on the rotational axis of the rotary cam. In the case of an SSCR mechanism, a separate spring is needed to return the oscillating mechanism to its base circle position.
For a second example, U.S. Pat. No. 6,311,659 discloses a Desmodromic Cam Driven Variable Valve Timing (DCDVVT) mechanism that includes a control shaft and a rocker. A second end of the opening rocker arm is connected to a control member. The rocker carries a first roller for engaging a valve opening cam lobe of an engine camshaft and a second roller for engaging a valve closing cam lobe of an engine camshaft. A link arm is pivotally coupled at a first end thereof to the first end of the opening rocker arm. An output cam is pivotally coupled to the second end of the link arm, and engages a roller of a corresponding cam follower of the engine. Thus, the valve opening and valve closing cam lobes cooperate to provide a positive opening and closing motion of the mechanism. While the engine valve return springs bias the rollers of the cam followers into contact with the output cam lobes, the cooperating valve opening and valve closing cam lobes avoid the need for a separate spring to return the oscillating mechanism to its starting position.
A shortcoming of these two prior art VVA systems is that both the SSCR device and the DCDVVT mechanism include two individual frame structures per each engine cylinder that are somewhat difficult to manufacture.
Another shortcoming is that the frame structures of these mechanisms “hang” from the engine camshaft and thus create a parasitic load.
An additional shortcoming of the SSCR mechanism is its significant reciprocating mass. The input rocker is connected through a link to two output cams that also ride on the input camshaft. Because the mechanism comprises four moving parts per cylinder, it is difficult to provide a return spring stiff enough for high-speed engine operation that can still fit in the available packaging space.
Still another shortcoming is that assembly and large-scale manufacture of such an SSCR device would be difficult at best with its large number of parts and required critical interfaces.
For a third example, U.S. Pat. No. 6,997,153 discloses a drive system for continuously changing lift characteristics of the charge-cycle valves while the engine is in operation. The drive consists of a housing, a cam, an intermediate element, and a valve-actuating output element. The cam is mounted in the housing, for example, in the cylinder head, in a turning joint and actuates the intermediate element which also is mounted in a turning joint in the housing. The intermediate element is connected to the output element via a cam joint formed at the contact point of the intermediate element, having a base circle portion (stop notch) and a control section, and the output element which may include a follower roller. The output element is also mounted in a turning joint in the housing and transmits motion to a valve stem. A change in valve lift characteristics is effected by changing the position of the intermediate element turning point or the output element turning joint via an eccentric element in the housing for either the intermediate element or the output element.
In the third example, while no indication is provided of a practical structure for implementing this arrangement, significant manufacturing and control complexity would exist in providing for, and controlling the action of, eccentric control shafts for both the intermediate and output elements.
What is needed in the art is a simplified VVA mechanism that is not mounted on the engine camshaft, is easy to manufacture and assemble, requires only a single angular control element, and requires minimal packaging space in an engine envelope.
It is a principal object of the present invention to provide variable opening timing, closing timing, and lift amplitude in a bank of engine intake and/or exhaust valves.
It is a further object of the invention to simplify the manufacture and assembly of a VVA system for such variable opening, closing, and lift.
It is a still further object of the invention to provide such a system which is not parasitic on the engine camshaft.